Implantable medical devices may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions, for example, chronic pain, tremor, Parkinson's disease, epilepsy, incontinence, or gastroparesis. Electrical stimulation therapy may be applied to deliver stimulation to any of a variety of tissue sites and may comprise, for example, neurostimulation, stimulation of muscle tissue, or the like. A medical device may deliver electrical stimulation therapy via a stimulator generator and one or more implantable leads that include electrodes located proximate to the spinal cord, pelvic nerves, stomach, or within the brain of a patient. The stimulation generator may be external or implantable. For chronic therapy, an implantable stimulation generator is typically desirable. In general, the medical device delivers electrical stimulation therapy in the form of electrical pulses, although continuous waveforms alternatively or additionally may be applied.
Spinal cord stimulation is used to alleviate chronic pain by stimulating the central nervous system using electrode arrays. Conventional spinal cord stimulator leads include percutaneous leads and surgical leads. Percutaneous leads are solid and have typically, four or eight electrodes. The percutaneous leads can be inserted through a needle and placed in the epidural space, in close proximity to the spinal cord. When activated, the electrodes deliver a precise, mild electrical impulse to the spinal cord or to a peripheral nerve. The electrical impulses activate pain inhibitory mechanisms to block the pain signal from reaching the brain.
Current designs of electrode arrays have had particular problems including, for example, lead migration, variable stimulation, and an inability to consistently stimulate deep fibers in the spinal cord. The stimulation of deeper midline structures is essential for treating low back pain. Further, multiple leads are required to cover large painful areas.
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